LTE is the 4th generation (4G) wireless data communication standard that supersedes WCDMA and other 3rd generation (3G) ones. Unfortunately, the far more diverse range of frequencies that the carriers around the world uses for this standard is a big headache, especially for Apple.

This is because a single model of iPhone tries to support as much of the entire world as possible in order to simplify the lineup. iPhone 4S, the last model before LTE support, indeed came in a single model for the entire world. In contrast, iPhone 5 and 5S had to be split up into multiple models that each had differing LTE band support. This was largely because the chipset couldn't support all the needed bands at once.

This meant that an iPhone bought in one country may not support LTE in another country. With iPhone 5, you needed model A1429 (for Sprint and Verizon in US) if you wanted it to use LTE in Korea. A1428 (for AT&T and T-Mobile in US) wouldn't do. That may have been a factor in the Korean carriers not automatically enabling LTE for foreign phones until 2014.

Situation is similar with iPhone 6S and 6S Plus, which adds a few more obscure or upcoming LTE bands on an already extensive array of support. There are still three specific models for each type, but one is for adding an upcoming AT&T-specific band 30 (A1633, A1634) and the other is for Chinese release (A1700, A1699). They are identical to the general model (A1688, A1687) otherwise.

However, not everything is in the clear. VoLTE (LTE-based voice calls) support is still not a universally supported feature among phones and carriers are still enabling this on a manual basis as of this writing. Owners of internationally bought iPhone 6, 6 Plus, 6S, and 6S Plus still need a visit to the carrier branch or store.

I had two iPhone 6S Plus that came from overseas - one is a "SIM-Free" version from Japan that you saw in my earlier post and the other is from United States intended for T-Mobile network. Both are model A1687 and the same version expected to be sold in Korea in a few days' time (October 23, 2015). The former was registered at an SK Telecom branch office as "OMD Apple VoLTE", the same title my iPhone 6 Plus received last year. The latter was registered at a local certified SK Telecom store as "OMD Apple VoLTE_6S" as shown here. Only after doing this, and waiting for a while to let the network know of the change, did the VoLTE function start to work.

The interesting (or cumbersome) part of doing the registration at a certified store was that it required me to have a separate, pre-registered device that was not in use to help with the registration. According to the store, once I inserted the SIM card into my iPhone 6S Plus, the network automatically registered it under "OMD Default Handset" because it wasn't recognized. In order to change that, the SIM card had to be put into another device so as to make the 6S Plus not be associated with any SIM card. Only then could the re-registration could proceed. Branch offices didn't have this requirement, so I have to assume that the system provided to the store is limited compared to the branch.

For nearly a month, I've been using my iPhone 6 Plus every day. As one of the first users of such device in Korea, I decided to take an in-depth look at its improvements and functions whenever I can, to show what the Korean users are going to get soon. Now all the hard work is done, and I present to you the summary of all the reviews I wrote about it.

iPhone 6 series will finally launch in Korea officially on October 31, 2014, according to Apple's official announcement, and carriers are preparing to accept pre-orders about a week before that. I hope these reviews will help you decide if iPhone 6 Plus is right for you.

Initially, all calls were made in 3G mode despite changing the settings to allow VoLTE. To have the VoLTE actually working, a visit to an SKT branch office and a device registration process was needed.

As I mentioned in the previous VoLTE post, all three major mobile carriers in Korea have been supporting VoLTE for quite some time now. One glaring problem, though, is that cross-carrier VoLTE still hasn't been realized, despite years of negotiations. This seem to have introduced some confusion. The truth is that a device can always request a VoLTE call, but it's up to the network to decide to go with it, and if so, fully or just on the surface.

In the case of LGU+, the carrier's aging "2G" CDMA network had been a weak point, so it worked hard to have everything done on LTE, even voice. That's why it'll accept a phone that can do VoLTE even if it doesn't support the needed CDMA frequency band - namely, the iPhone 6 series. ( One caveat is that they are not accepted for registration on the network yet until official Korean debut. This is largely a decision of policy, not technicality. ) If you have such a phone, all calls will be connected as VoLTE no matter what.

But in case of SK Telecom (SKT) or KT, their "3G" WCDMA networks are still widely used. So they don't have the urge to go fully LTE. A call could still be made on either 3G or LTE, depending on the situation. No handsets on these networks get to make all of its calls on VoLTE.

Since I'm on SKT, I made calls to various phone numbers on my VoLTE phone, iPhone 6 Plus, to see how they end up connecting, and what quality they were.

Case

Caller 1

Caller 2

Connect 1

Connect 2

Quality

1

SKT VoLTE

SKT VoLTE

LTE

LTE

HD Voice

2

SKT VoLTE

SKT 3G (AMR-WB)

LTE

3G

HD Voice

3

SKT VoLTE

SKT 2G/3G

LTE

2G/3G

Normal

4

SKT VoLTE

KT / LGU+ VoLTE

LTE

LTE

Normal

5

SKT VoLTE

KT / LGU+ 2G/3G

LTE

2G/3G

Normal

6

SKT VoLTE

Landline (02 ~ 064)

LTE

Landline

Normal

7

SKT VoLTE

Toll Free (080)

LTE

Landline

Normal

8

SKT VoLTE

Special (15xx, 3-digit)

3G

Landline

Normal

9

SKT VoLTE

VoIP (070)

3G

Internet

Normal

As of this writing, two types of phones on the SKT network, the VoLTE-enabled phones (case 1) and the AMR-WB supported phones without VoLTE (case 2), can make end-to-end HD Voice-quality calls to and from iPhone 6 Plus. AMR-WB codec is the same codec used by VoLTE, but some phones support this only on 3G at a lower bitrate, e.g. iPhone 5 and Xperia Ray.

As mentioned earlier, cross-carrier VoLTE agreements are not yet in place, so calling VoLTE phones on other networks (case 4) ends up degrading quality. I'm hoping this clears up soon because there's no technical reason to be like this.

Meanwhile, most calls connect via LTE, with the exception of special numbers such as the three-digit numbers (including emergency) and the 15xx, 16xx numbers that companies use (case 8), as well as the VoIP numbers with the 070 area code (case 9). I understand that these numbers don't connect with high-quality codecs so LTE connection isn't necessary, but it doesn't explain why regular landline connections do connect via LTE.

Cellular communications have traditionally used separate voice and data channels. But with the advent of smartphones, bulk of the communications now happen on the data channel. It's no coincidence that only the data channel remained by the 4th generation (4G) technology. To carry voice, though, a fallback to 3G or older technology's voice channel was initially needed. But VoLTE (Voice over LTE) came onto the scene to do away with this by letting the data channel handle voice as well.

As with many technologies, Korea was a forerunner in adopting VoLTE. World's first commercial VoLTE service was launched more than two years ago by two of the three major Korean carriers, SK Telecom and LG U+. The remaining one, KT, joined mere two months later. Worldwide adoption didn't really take off until earlier this year, however. About a dozen carriers around the globe now have it. Noting this trend, Apple has decided to enable the capability in the iPhone 6 series.

So naturally, I wanted to see VoLTE on my iPhone 6 Plus in action. It can be enabled in the Settings app by going to Cellular and selecting "Voice and Data" option for LTE. The previous 5/5C/5S models simply have toggle switch for LTE instead, even with iOS 8.0 update. After that, I made voice calls to a lot of different lines, including a VoLTE-enabled phone on the same carrier. But every time, the connection indicator turned from LTE to 3G, showing that VoLTE wasn't working.

iPhone 6 Plus seen as "OMD Default Handset"

I checked to see how the network recognized my iPhone 6 Plus. It was being listed as an OMD Default Handset, the same name that my iPhone 5S was given when it was brought in from the US. In other words, a generic device that it doesn't recognize. Perhaps the network couldn't tell whether the device had a VoLTE capability, so it simply ignored its attempts. It was time to visit my carrier's branch office to get to the bottom of this.

LTE frequencies tend to be quite varied because it has to be either laid alongside or replace the existing 2G and 3G networks. Even so, Apple tries to support as much frequencies as possible because it will reduce the number of region-specific models. Unfortunately, iPhone 5S and 5C each sprawled to five different models, so people asked around whether their iPhones would work on another country's LTE network. I even wrote about iPhone 5S's LTE network compatibility last year, and it has the longest comment thread in this website.

This time around, though, the number of models were reduced to a much more manageable two for both iPhone 6 and 6 Plus. The massive 20-band support did the trick. The good news here is that, if you bought an unlocked iPhone 6 or 6 Plus anywhere in the world and come to Korea, the LTE will work with all three local carriers. Korea should get A1586 / A1524 models on sale in a couple of months, but A1549 / A1522 models often found in United States or Canada should work, too.

After I brought the A1524 iPhone 6 Plus from Japan to Korea, I put the SIM card from my 5S and turned it on. The device had no problems connecting to SK Telecom's LTE network right away. I've confirmed that the situation is the same when you're on KT's network, as well. It seems that the network no longer goes into 3G mode when it sees an unrecognized LTE device, which used to be the case when I brought the iPhone 5S from United States last year.

iPhone 6 Plus hitting 96Mbps download on LTE

Meanwhile, the top speed for LTE data on iPhone 6 series was pushed to 150Mbps from 100Mbps of 5/5C/5S. The bleeding edge phones in Korea are always a step ahead - 150Mbps was possible when iPhone 5 came out and the recent models can do 225Mbps - but with low monthly data caps, they are little more than technology show-off right now.

In any case, I wanted to see how fast the iPhone 6 Plus can do LTE data in real life, so I ran a speed test app. As you can see here, it can go almost up to 100Mbps. Pretty good, but that's how fast an iPhone 5S could supposedly do, as well. Obviously, a side-by-side test was needed.